Additive manufacturing (AM) is pivotal in advancing in-situ resource utilization (ISRU) technologies for space exploration, enabling the construction of lunar infrastructure directly from local materials such as lunar regolith. Among the various AM techniques, laser-based directed energy deposition (DED-LB) offers scalability and binder-free processing, making it highly suitable for fabricating large-scale components on the Moon. However, the limited availability of actual lunar regolith necessitates the use of simulants. Mullite, an aluminosilicate ceramic with a chemical composition closely resembling that of highland lunar regolith, is a promising candidate. In this study, synthetic mullite with a spherical morphology was employed as a model feedstock to investigate the feasibility of fabricating multilayer 3D printed components using the DED-LB process. The high thermal stability and round particle morphology of mullite make it an ideal proof-of-concept material to understand the thermal and mechanical challenges associated with lunar regolith printing. A combination of in-situ thermal monitoring and microstructural characterization was used to define optimal process parameters and assess print quality. The results demonstrate the suitability of mullite for DED-LB and contribute to the development of scalable AM processes for future lunar infrastructure.